Cigarettes having ventilating openings in mouthpieces or filters at the aspiration end of the cigarette and in the wall or opening thereof are commonly available and are intended to permit the smoker, as he inhales, to induce ambient air into the mouthpiece or filter and into the mouth of the smoker to dilute the smoke. This is intended to create the effect of a light cigarette by decreasing the density of the smoke reaching the user.
In practice, however, it is found that the level of nicotine in cigarettes increases substantially from the beginning of smoking toward the end of the cigarette. When air is drawn at a constant rate into admixture with smoke, therefore, the rest of the cigarette varies over the direction of smoking, because the composition of the smoke changes, i.e. the nicotine is more greatly diluted at the beginning of smoking and is subjected to lesser dilution toward the end of the cigarette. A cigarette which can be considered a light smoking cigarette at the start may be found to be a strong cigarette at the end.
It has been proposed, e.g. in U.S. Pat. No. 4,327,748, to provide a cigarette holder having a manually controllable valve which is intended to regulate the amount of air induced into the inhaled smoke in accordance with the wishes of the smoker and hence the personal tastes. This, however, does not solve the problem of increasing nicotine concentration unless the user is willing to continuously vary the valve position as the particular cigarette is smoked. This, of course, is impractical and hence generally a single setting is selected for a particular type of cigarette to avoid adjustment over the duration of smoking, i.e. for the extent to which cigarettes are smoked for each smoked cigarette.
In U.S. Pat. No. 3,441,028, moreover, a cigarette holder has been described in which the smoke passage is provided with a constriction having a metallic valve responsive to the temperature and adapted to control the introduction of air into the smoke. A filter in this cigarette holder is disposed downstream of the valve to trap components of the smoke which condense by cooling as a consequence of the admission of air.
This system has the disadvantage that it is difficult to provide a bimetallic control which is sufficiently sensitive to react to the very small temperature differences which are found in the cigarette smoke. Indeed, the temperature of the smoke varies very little during the consumption of a cigarette so that the change in temperature cannot be considered truly a parameter which parallels the concentration of nicotine in the smoke.